If you reload, it's tough to beat a 308. You can always load it down with 125 bullets at moderate velocities.

I like the 7-08 or 270 with reduced recoil ammo (or reduced loads if you hand load). They won't kick much more than a 243 and he can move up in power as he gets older. I would also suggest getting a youth stock that fits him. They're kinda hard to find but you can find a cheap one on eBay and have a gunsmith cut it down. Then when he gets older you can put the original one back on and he's ready to rock. He'll get years of service from the same rifle. Good luck!

I agree with deewayne2003. Start them off on smaller calibers and work your way up.

Most people tend to overlook the simple fact that "youth" guns are typically shorter LOP and light weight - tapered barrels, synthetic stocks, etc - basically empt,y short barreled, light rifles. They get one that "feels" good/comfortable to the young shooter in caliber "X". Then the parents go buy a box of rounds off the shelf that for that caliber and we're off!!

Most people don't think about the felt recoil of the same round in their rifle with a solid wood stock, long barrel, large scope, sling and bipod on it. Compare that to the stripped down, lighter and shorter version you're giving to the kid.

Manage recoil with getting a youth variant with some substance to it (wood stocks or fill the back of the synthetics with a sand/epoxy resin, etc.), recoil pads, or managed recoil rounds in the caliber chosen.